Field of the Invention
The present invention relates to media for stem cells, a method of producing such a medium, and the like.
Discussion of the Background
Conventionally, the culture of stem cells (embryonic stem cell, induced pluripotent stem cell (iPS cell) and the like) has been conducted using a medium containing a serum. For example, fetal bovine serum (FBS) and the like are widely used for cell culture as an important additive for cell proliferation. However, when stem cells after culture are used for medical purposes, a xeno-derived component may become a source of infection with blood-borne pathogen or a xenoantigen. In addition, culture results may be inconsistent due to differences between serum lots. Therefore, it is mainstream in recent years to use a medium having a clear chemical composition (chemically-defined medium) for culturing stem cells, and the development of a serum-free medium is ongoing.
One of the highly important components for serum-free medium is albumin. Addition of albumin is expected to provide an effect of stably maintaining the medium property. Several kinds of albumin are commercially available for culturing cells. However, albumin is comparatively expensive, not all albumins provide an equivalent effect for cell culture, particularly culture of stem cells, and the quality of albumin affects the culture results; in some cases, addition of albumin unfavorably acts on the cell growth. Furthermore, degradation of albumin in the medium has also posed a problem.
As a comparatively economical albumin, an albumin extracted from a serum of animals such as human, bovine and the like can be mentioned. However, when the donor is infected with a virus and the like, the risk of dissemination thereof exists. Therefore, use of such albumin derived from animal serum for clinical application is markedly limited and, even when use is permitted, the amount thereof to be used is required to be extremely low.
Albumin produced by a gene recombination (recombinant) method considered to be preferable for use for clinical application due to its low infection risk is considerably expensive. When a sufficient amount of cells is to be secured by subjecting such albumin to cell culture, the cost becomes extremely high. To use such recombinant albumin in cell culture, therefore, the amount thereof to be used is required to be extremely small.
Accordingly, the development of a medium using a reduced amount of albumin or free of albumin has been tried. For example, JP-A-2004-135672, which is incorporated herein by reference in its entirety, reports on the use of polyethylene glycol as an albumin substitute in a medium. JP-A-2007-228815, which is incorporated herein by reference in its entirety, reports on a polyvinyl alcohol-containing medium characteristically free of albumin. US 2010/0317104A1, which is incorporated herein by reference in its entirety, reports on the use of polyvinyl alcohol in a medium for embryonic stem cells (HESCs). WO 2011/100286A2, which is incorporated herein by reference in its entirety, reports that polyvinyl alcohol and the like are used in a medium for differentiation of mesoderm stem cells from pluripotent cells.
However, there remains a need for improved culture media for culturing stem cells.